1. Field of the Invention
The present invention relates to a data reproducing apparatus such as a VTR (video tape recorder) capable of reproducing recorded data in a non-tracking reproducing fashion and a data reproducing method thereof.
2. Description of the Related Art
In recent years, in the recording format of the VTR, recording density is increased more in response to the demand of improving quality of image increasingly. To this end, a track pitch of a video tape is extremely decreased to be less than 10 μm.
As the track pitch is narrowed extremely as described above, even when the same track is scanned only once by one reproducing head (“just-tracking reproduction”), due to very small extension and contraction of the video tape and mechanical accuracy of a tape transport system, an off-track amount exceeds a range in which reproduced data can be error-corrected by C1 error correction (error-correction using inner parity) and hence recorded data cannot be reproduced accurately.
Accordingly, “non-tracking reproduction” exists as a reproducing method suitable for such case. In this non-tracking reproduction, after the same track was scanned by a plurality of reproducing heads or the same track was scanned by a single reproducing head a plurality of times and reproduced data obtained by the above-mentioned scanning was error-corrected by the C1 error correction, only reproduced data error-corrected by this C1 error correction was written in a memory and data read out from this memory is error-corrected by C2 error correction (error-correction using outer parity).
FIGS. 1A and 1B of the accompanying drawings are respectively schematic diagrams showing the range in which data reproduced by the non-tracking reproduction can be error-corrected by C1 error correction in contrast with the range in which data reproduced by the just-tracking reproduction can be error-corrected by C1 error correction.
In the case of the just-tracking reproduction in which the same track tr is scanned by one reproducing head A only once as shown in FIG. 1A, an off-track range (shown hatched in FIG. 1A) in which reproduced data can be error-corrected by C1 error correction is narrow. On the other hand, in the case of the non-tracking reproduction in which the same track tr is scanned by two reproducing heads A1 and A2 (reproducing heads with equal azimuth angles) as shown in FIG. 1B, reproduced data can be completely error-corrected in the off-track range (shown hatched in FIG. 1B) in which reproduced data can be error-corrected by C1 error correction.
In the VTR, splice editing for splicing other image to a certain scene of the previously-recorded image or insert editing for inserting other image into a certain range of the previously-recorded image are carried out frequently. If the track pitch is very narrow, then upon editing, a recording head is off-tracked from the track in which image was previously recorded so that the track in which image was recorded previously cannot be erased and remains inerasable although it should be erased by overwriting. For simplicity, the track in which image was recorded previously will hereinafter be referred to as a “previously-recorded track”.
FIGS. 2A to 2C are schematic diagrams used to explain the above-mentioned inerasable previously-recorded track. As shown in FIG. 2A, 48 video tracks VT divided into upper and lower sectors and 8 audio tracks AT provided between the upper and lower sectors of the video tracks VT are handled as a segment SE which is the minimum unit of editing.
FIG. 2B shows the state in which the recording head is not off-tracked from the previously-recorded track upon insert editing using one central segment SE in FIG. 2A as an object to be edited. At that time, since an edit portion (portion in which data is recorded actually upon editing) is completely overlapping with the segment SE to be edited, the previously-recorded track which has been recorded on the segment SE to be edited is completely erased by overwriting and the inerasable previously-recorded track does not exist (the previously-recorded tracks at both sides of the edit portion are the previously-recorded tracks recorded on other segments adjacent to the segment SE that should be edited).
On the other hand, FIG. 2C shows the state in which the recording head is off-tracked from the previously-recorded track upon insert editing using one central segment SE in FIG. 2A as an object to be edited. At that time, since the edit portion is shifted from the segment SE that should be edited, the previously-recorded track recorded on the segment SE to be edited is left inerasable.
When the video tape with the inerasable previously-recorded track left thereon as shown in FIG. 2C is reproduced by the non-tracking reproduction, inerasable previously-recorded tracks error-corrected by C1 error correction are collected and further error-corrected by C2 error correction. As a result, C2 error correction capability is lowered and hence it becomes impossible to reproduce the edited data correctly.
As described above, in the non-tracking reproduction, it becomes important to exclude the inerasable previously-recorded track from the track that should be error-corrected by C2 error correction. As a method for excluding the inerasable previously-recorded track from the track that should be error-corrected by C2 error correction, there has been so far proposed a method of inserting edit data ID (Edit ID), which is used to identify the inerasable previously-recorded track, into ID (identification data) of SYNC (synchronizing) block and which method uses the Edit ID (for example, see cited patent references 1 and 2).
[Cited patent reference 1]: Official gazette of Japanese laid-open patent application No. 9-266563
[Cited patent reference 1]: Official gazette of Japanese laid-open patent application No. 9-312090
Specific examples of the above-mentioned method according to the related art will be described with reference to FIGS. 3 and 4. FIG. 3 is a schematic diagram showing an example of the Edit ID, inserted into the ID of the SYNC block, together with an ECC (error correction code) block composed of the predetermined number of SNYC blocks. An Edit ID (ID2) of 8 bits for identifying the inerasable previously-recorded track is inserted into the ID of the SYNC block together with a sync number (ID0), a track number (ID1), etc.
FIG. 4 is a block diagram showing a recording and reproducing system of a non-tracking reproduction system VTR according to the related art which can exclude the inerasable previously-recorded track by using this Edit ID.
As shown in FIG. 4, this VTR includes a recording system comprising a video compressor 51, a SYNC/ID/parity adder 52, recording circuits 53 and 54 and recording heads 55 (a head A with a positive azimuth angle and a head B with a negative azimuth angle).
Also, this VTR includes an ordinary reproducing system (video/audio reproducing system) comprising reproducing heads 56 (heads A1 and A2 with positive azimuth angles and heads B1 and B2 with negative azimuth angles), equalizing and decoding circuits 57 to 60, C1 error correctors 61 to 64, a non-tracking processing circuit 65, an Edit ID detector 66, a C2 error corrector 67 and a video expander 68.
Also, independently of the above-mentioned ordinary reproducing system, this related-art VTR includes a reproducing system for detecting the Edit ID from the previously-recorded track. This reproducing system is composed of advance heads 69 (heads A1 and A2 with positive azimuth angles and heads B1 and B2 with negative azimuth angles) for reproducing the previously-recorded track prior to the recording of the edit portion, equalizing and decoding circuits 70 to 73, C1 error correctors 74 to 77 and a previously-recorded track Edit ID detector 78.
In this VTR, upon normal recording (when the previously-recorded track is made), after a video signal to be recorded was band-limited by the video compressor 51 and compressed by bit reduction, the SYNC/ID/parity adder 52 adds SYNC, ID, inner parity and outer parity to the resultant compressed video signal as shown in FIG. 3 to constitute the SYNC block/ECC block.
Also, in a like manner, the SYNC/ID/parity adder 52 adds SYNC, ID, inner parity and outer parity to a non-compressed audio signal to be recorded to constitute the SYNC block/ECC block.
Then, output data from the SYNC/ID/parity adder 52 are respectively converted into recording currents by the recording circuits 53, 54 and recorded on a video tape TP by the recording heads 55.
After the previously-recorded track was made as described above, upon editing, prior to the recording of new video/audio signals, signals reproduced from the video tape TP by the advance heads 69 are respectively equalized, decoded and C1 error-corrected by the equalizing and decoding circuits 70 to 73 and the C1 error correctors 74 to 77, and Edit IDs are detected from the output data of the C1 C1 error correctors 74 to 77 by the Edit ID detector 78.
Then, the SYNC/ID/parity adder 52 adds SYNC, ID, inner parity and outer parity to the Edit ID, which results from adding “1” to the Edit ID detected by the previously-recorded track detector 78 to the video signal compressed by the video compressor 51 and the non-compressed audio signal, to thereby construct the SYNC block/ECC block.
Then, output data from the SYNC/ID/parity adder 52 are respectively converted into recording currents by the recording circuits 53, 54 and recorded on the video tape TP by the recording heads 55.
On the other hand, upon reproduction, reproduced signals reproduced from the video tape TP by the reproducing heads 56 are respectively equalized, decoded and C1 C1 error-corrected by the equalizing and decoding circuits 57 to 60 and the C1 error correctors 61 to 64 and output data from the C1 error correctors 61 to 64 are supplied to the non-tracking processing circuit 65. At the same time, the Edit ID is detected from the output data of the C1 error correctors 61 to 64 by the Edit ID detector 66.
The non-tracking processing circuit 65 carries out the non-tracking processing. That is, of the reproduced data C1 error-corrected by the C1 error correctors 61 to 64, data of the SYNC block in which the Edit ID detected by the Edit ID detector 66 agrees with the Edit ID added upon editing is written in a memory (not shown) but data of other SYNC blocks are not written in the memory and data read out from this memory is supplied to the C2 C2 error corrector 67. Thus, the inerasable previously-recorded track can be excluded from those to be C2 C2 error-corrected by the C2 C2 error corrector 67.
Then, the reproduced data from the non-tracking processing circuit 65 is C2 error-corrected by the C2 error corrector 67 and video data of the output data from the C2 error corrector 67 is expanded by the video expander 68, whereby a reproduced video signal and a reproduced audio signal can be obtained.
However, according to the above-mentioned related-art method, since the Edit ID is inserted into the ID of the SYNC block, it is unavoidable that the bit number of the ID is increased (8 bits are increased in the example shown in FIG. 3). Then, there is a disadvantage in which substantial recording densities of the video and audio signals are lowered.
Further, as shown in FIG. 4, since the data reproducing system (VTR) according to the related art should include the reproducing system (reproducing heads and signal processing circuits) exclusively-designed for detecting the Edit ID from the previously-recorded track, there are disadvantages in which a rotary drum becomes difficult to be miniaturized and in which a circuit arrangement becomes complex.